In recent years, an imaging device having a function of shooting a movie has become popular. Sound generated during the shooting of a movie sometimes includes noise. For example, the driving sound of an auto-focusing lens corresponds to noise. In particular, such driving sound is loud in a lens barrel which is not designed in consideration of the movie shooting, in which case the noise increases. In view of this, a noise reduction process may be performed.
For example, there is a technique (VAD: Voice Activity Detection) for distinguishing a sound signal including human voice (voice section) from a sound signal excluding human voice (non-voice section) by emphasizing and extracting the human voice included in sound signals collected with a microphone (see Patent Document 1). The noise can be suppressed by calculating estimated noise with the use of the sound signal in the non-voice section and subtracting the estimated noise from the sound signal utilizing VAD (for example, see Patent Document 1).
During the shooting of a movie with an imaging device capable of shooting a movie, the noise such as the operation sound caused along with the operation of a drive unit of the auto-focusing lens (hereinafter, AF noise) might be collected by a sound collection device such as a microphone and mixed in with target sound such as the voice of a subject, in which case the quality of the target sound is deteriorated.
As a method of reducing the AF noise as above, a method for reducing the noise has been suggested in which a power value of a voice signal input before the operation of the AF drive unit is obtained and the flooring coefficient is controlled (varied) on the basis of the power value of the voice signal (for example, see Patent Document 2).    [Patent Document 1] Japanese Unexamined Patent Application, Publication No. 2009-294537    [Patent Document 2] Japanese Unexamined Patent Application, Publication No. 2008-252389